1. Field of the Invention
The present invention relates to a recording apparatus of serial type, and more particularly to a recording head having a heat generating portion for generating thermal energy to be used for recording and an apparatus provided with such recording head.
2. Related Background Art
The recording apparatus of ink jet system executes recording by discharging a droplet of recording liquid (ink) from a discharge port of a recording head and depositing such droplet onto a recording medium. In the recording apparatus employing such ink jet system, for example a serial ink jet printer, the recording is executed by discharging ink from the recording head while it is moved in a main scanning direction and conveying the recording medium by a recording medium conveying member (roller) between the scanning motions.
Among the recording heads, there is known a recording head for discharging a micro droplet of liquid utilizing thermal energy generated for example by an electrothermal converting member and a recording head for discharging a liquid droplet by deflection with a pair of electrodes. Among these heads, the recording head discharging liquid droplet by utilizing thermal energy is provided with advantages such as that recording of a high resolution is possible because the ink discharging portions (discharge ports) can be arranged with a high density and that the entire recording apparatus can be easily compactized, and is therefore commercially utilized. FIG. 15 is a perspective view showing an example of a serial ink jet recording apparatus, in which the recording head thereof is provided with a head casing, having detachable ink tanks 50. The head casing 51 is provided, on a rear face thereof (opposite to a face on which the ink tank 50 is mounted), with an ink supply portion 55 having ink flow paths communicating with ink supply apertures of the ink tanks 50 respectively through liquid chambers, and discharge portions 52 are provided on the ink supply portion 55 across a support member (heat dissipating member) 54.
The ink supply portion 55 and the support member 54 are mutually fixed by adhesion, and the support member 54 and the discharge portions 52 are mutually fixed by adhesion. The support member 54 is provided with plural ink flow paths for supplying the discharge portions 52 respectively with inks, and these ink flow paths are respectively connected with those of the ink supply portion 55. Since the precision of the discharge portions 52 is extremely important, the support member 54 has to be composed of a material of high heat resistance and high flatness and is generally composed of a metal or a ceramic material.
Each discharge portion 52 is provided with plural discharge ports arranged with a predetermined pitch in a longitudinal direction (crossing the scanning direction (for example, perpendicularly)), and an energy conversion element such as an electrothermal converting element is provided for each discharge port. The discharge portion 52 is electrically connected with a flexible cable 53 through which electrical signals for driving the energy conversion elements are supplied from an unrepresented control unit. In order to reduce the electrical resistance, the flexible cable 53 usually has an area approximately equal to a discharge surface of the support member 54 (a surface of support member 54 facing discharge portions 52) and is so provided as to cover the discharge surface of the support member 54.
The recording head shown in FIG. 15 is provided with a discharge portion 52 for each ink tank 50, and the number of such ink tanks and discharge portions is variable depending on the specifications.
In the following there will be given a more detailed description of the structure of the discharge portion of the conventional recording head. FIGS. 16A and 16B are respectively a perspective view and an exploded perspective view of the discharge portion of a conventional recording head, wherein the discharge portion 52, the support member 54 and the ink supply member 55 are basically similar to those shown in FIG. 15 except for a difference in the shape and in the number of ink flow paths.
The support member 54 is provided with plural ink flow paths 54a, and the discharge portions 52 are fixed by adhesion on each of the ink flow paths 54a, respectively. The ink supply portion 55 is composed of a molded member (for example, of organic resinous material) and is provided with plural ink flow paths 55a respectively corresponding to the ink flow paths 54a of the support member 54, and the support member 54 is fixed by adhesion in such a manner that the corresponding ink flow paths are mutually connected. The adhesion between the discharge portions 52 and the support member 54, and between the support member 54 and the ink supply portion 55, is achieved by an adhesive material of a very high thermal conductivity.
Each discharge portion 52 is provided with plural discharge ports in the longitudinal direction thereof (crossing the scanning direction (for example, perpendicularly)), and an electrothermal converting element is provided for each discharge port. At ink discharge, an electrical pulse is applied according to drive data to the electrothermal converting element of each discharge port, whereby film boiling is generated in the ink and the ink is discharged from the discharge port by the growth of a bubble generated by the film boiling.
The heat generated in such ink discharge is considered to be dissipated principally by the following three processes:
(1) heat dissipation to the discharged ink itself;
(2) solid heat conduction from the discharge portions 52 to the support member 54 and the ink supply portion 55; and
(3) heat dissipation from the discharge portions 52, the support member 54 and the ink supply portion 55 to the external space (air).
In the conventional recording head, as explained in the foregoing, the heat generated in the discharge portions 52 at ink discharge is partly taken away by the discharged ink droplet itself and is dissipated by solid heat conduction and heat dissipation. In the aforementioned conventional recording head, the heat movement is generally much faster and larger in the solid heat conduction to the support member 54 than in the heat dissipation to the air. Consequently the heat generated in the discharge portions 52 is immediately transmitted to the support member 54. However, since the material employed in the ink supply portion 54 generally has a low heat conductivity, the solid heat conduction from the support member 54 to the ink supply portion 55 is not performed effectively, so that the heat transmitted to the support member 54 is eventually dissipated from the surface thereof into the air. In this manner, the cooling or heat dissipation in the conventional recording head principally relies on the heat dissipation from the surfaces of the discharge portions 52 and the support member 54 except for the part of the heat dissipated by the discharged ink droplet itself. For this reason, heat tends to accumulate in the head and, since the heat capacity is not so large, there easily results an increase in the temperature. Especially in a configuration in which the surface of the support member 54 is covered by the flexible cable 53, heat tends to accumulate more in the head, thus leading to a further temperature increase, because an additional process of heat conduction from the support member 54 to the flexible cable 53 is required.
An excessive increase in the temperature of the head may result in the following drawbacks:
(1) ink cannot be discharged (non-discharge);
(2) bursting of ink droplet at discharge;
(3) accelerated kogation and deterioration of the electrothermal converting element (heat generating member or heater); and
(4) fluctuation of recording density in recording on a recording medium such as paper.
It is therefore an important issue how to suppress the temperature increase of the recording head.
The most common countermeasure against temperature increase is to provide a pause between the scanning motions when the recording head shows a certain temperature increase and to dissipate the heat during such pause. This method however requires a long pause for cooling, and the recording time required for each recording sheet is extended by such pause, thus resulting in a significant reduction in the recording speed.
It is effective to cool a recording head showing temperature increase by heat generation at ink discharge, with a fan, and there is already proposed a configuration in which a fan is fixed to a carriage supporting the recording head. In such configuration, however, the carriage becomes heavier because the fan is fixed thereto, and it becomes difficult to increase the driving frequency. Also, as the ink droplet becomes finer, the air flow generated by the fan and directed toward the recording head may result in an aberration in the landing position of the ink droplet and in ink drying in the discharge portions.
There is also conceived a method of air cooling the recording head with an air flow generated by the movement of the carriage, instead of employing the fan. As an example, Japanese Patent Application Laid-open No. 2000-141819 proposes a cooling mechanism having a cooling air path between a head heat dissipation plate provided in the head unit of the ink jet printer and an internal lateral wall of the carriage opposed to the aforementioned head heat dissipation plate. In this cooling mechanism, an air flow is generated in the cooling air path by the carriage movement, and the air flows along the surface of the head heat dissipating plate, thereby achieving efficient heat dissipation by the head heat dissipation plate. However, such cooling mechanism is insufficient for air cooling the vicinity of the ink discharge port having a large amount of heat within the head unit, because the head heat dissipation plate is provided in a position distant from the ink discharge port.
In addition to the foregoing, there have been proposed methods for cooling the recording head with liquid. As an example, Japanese patent No. 2738697 (Japanese Patent Application Laid-open No. 01-242257) proposes:
(1) method of winding a tube around the liquid discharge recording head and flowing cooling liquid in such tube;
(2) forming a liquid flow path in a substrate bearing the thermal energy generating portion and flowing liquid in such liquid flow path; and
(3) forming the thermal energy generating portion on a substrate composed of a porous material and having a heat accumulating layer thereon and impregnating the porous material with cooling liquid.
However, these cooling methods inevitably complicate the apparatus and result in a high cost, because there are required means for supplying the tube, flow path or porous member with the cooling liquid and means for replacing and discarding the cooling liquid.
Also the recent progress in recording speed and in image quality results in an increase the density of the ink discharge nozzles and the input energy, and in a decrease in the heat dissipating space, thus leading to a situation more unfavorable for the temperature increase in the recording head. The issue of temperature increase in the recording head is becoming unavoidable also based on such technical background.
The present invention relates to a liquid discharge recording head for executing recording by moving in opposed relationship to a recording medium and discharging liquid from a discharge port, provided with energy generation means capable of generating thermal energy for discharging ink, a heat dissipating substrate positioned substantially parallel to the energy generation means and capable of transmitting the heat of the energy generation means, and a support member for supporting the heat dissipating substrate, the recording head further comprising a space continuous in the moving direction of the recording head between the support member and the rear surface of the heat dissipating substrate opposite to the surface thereof on which the energy generating means is provided. The present invention also relates to a recording apparatus provided with a carriage capable of supporting a liquid discharge recording head for executing recording by moving in opposed relationship to a recording medium and discharging liquid from a discharge port by thermal energy, wherein the recording head comprises a duct penetrating (extending) in a predetermined direction the surface of a member provided with means for generating thermal energy, the aforementioned surface being opposite to the surface on which the thermal energy generating means is provided.
According to the invention mentioned above, the heat generating portion can be cooled both from the head surface and from the inside of the head with the movement of the recording head.
In the present invention, in a configuration having a heat transporting means and a heat dissipating means, the heat accumulated inside the recording head among the heat generated in the heat generating portion is removed to the outside of the head by the heat transporting means and is radiated by the heat dissipating means.
Also, according to the present invention, as the recording head is opposed to a cooling fan in a predetermined position where the cooling fan causes an air flow in the duct or blows an air flow to the heat dissipating means, the head can be cooled more efficiently and within a shorter time in comparison with the conventional configuration employing an air cooling fan. Consequently, even if the recording head is excessively heated and is subjected to a forced air cooling operation with a cooling fan, cooling can be achieved within a short time and the recording speed is not sacrificed.
As explained in the foregoing, the present invention avoids complication of the apparatus and cost increase as in the conventionally employed cooling means, by merely providing the recording apparatus with a duct and more preferably with a cooling fan.